This invention relates to camshaft arrangements having a cam which can be hydraulically coupled to a camshaft.
Camshaft arrangements with deactivatable cams provide a number of advantages since they permit inlet or outlet valves to be rendered active or inactive according to the prevailing operating conditions of an engine by activation or deactivation of the associated cams. Thus, in engines having two intake valves for each cylinder with cams providing different valve opening times, it may be expedient to have both intake valves activated only at higher engine speeds, whereas, at lower engine speeds, one of the two valves is kept closed while the other valve is actuated in the usual manner by an associated cam which has a configuration optimized for low engine speed. Such a camshaft arrangement may also be used in internal combustion engines with a cylinder cut-out arrangement. In such engines, all inlet valves for one or more combustion chambers are kept closed in an economy mode selectable by the operator, for example, in which their associated cams are deactivated. In this condition, the engine will operate at partial load on only some of its cylinders.
Camshaft arrangements having at least one deactivatable cam are disclosed, for example, in German Offenlegungsschrift No. 39 20 938. These conventional designs operate with sleeves which are components of jaw couplings individual to certain cams and are axially slidable on the camshaft in response to pressure applied by a hydraulic medium. When the jaw couplings for a cam are moved into engagement by axial motion of the corresponding sleeve, there is a rotationally fixed connection between the cam, which is otherwise deactivated, and the camshaft. Such a camshaft arrangement may be provided if there is room enough in the axial direction of the camshaft to accommodate the displaceable coupling components for each of the deactivatable cams.
The copending Voigt U.S. application Ser. No. 07/896,625, filed Jun. 10, 1992, of which this application is a continuation-in-part, discloses a camshaft arrangement having at least one deactivatable cam mounted on a camshaft with a coupling which includes a coupling pin displaceable in a transverse, approximately radial recess in the camshaft between an engaged position, in which it engages an inner coupling recess in the cam to establish a rotationally fixed connection between the cam and the camshaft, and a release position, in which it is withdrawn from the coupling recess to disconnect the cam from the camshaft. The end of the coupling pin opposite from the coupling recess, i.e., the rear face, together with the recess in the camshaft, forms a pressure chamber which communicates with a supply of hydraulic fluid within the camshaft, and the coupling recess in the cam has an associated pressure relief such as an opening to atmospheric pressure. Such a camshaft having coupling pins which are displaceable at least approximately radially has the advantage of a short structural length while providing for deactivatability of at least one cam.
Because of the high rotational speeds of camshafts in internal combustion engines, such as those for motor vehicles, and the corresponding centrifugal forces, however, difficulties may be encountered in assuring precisely timed motion of the coupling pin between its two positions in such deactivatable cam arrangements.